1. Field of the Invention
The present invention relates to a fluid drive unit for vibrating fluid, which is charged in a passage, in the direction of the passage. The present invention also relates to a heat transport system in which the fluid drive unit is used.
2. Description of the Related Art
As is well known, heat is conducted from a high temperature portion to a low temperature portion in proportion to temperature gradient ΔT according to the Fourier's Law. In this case, the proportional constant is referred to as heat conductivity, which changes according to the medium in which heat is conducted. However, even in mediums including gas, liquid and solid, heat conductivity changes only by five digits. Therefore, when heat is transported, the quantity of heat to be transported is restricted.
In order to overcome this problem, investigations have been recently made into a method in which heat is efficiently transported by vibrating a fluid. This method of transporting heat utilizes the following principle. In this connection, FIGS. 22A, 22B and 22C are schematic illustrations to show the principle of transporting heat.
In order to briefly explain this principle, the following circumstances are established. Fluid is filled in a circular tube, and vibration center C of the fluid in the circular tube is set as a reference point. A low temperature portion is present at point L on the left of center C, and a high temperature portion is present at point H on the right of center C. A portion of the fluid, which is present at vibration center C in the case where no vibration is caused, is defined as element E. In the above circumstances, consideration is given to a rectangular wave vibration in which the element E stays at point H for a half period and immediately moves to point L and stays there for a half period and then immediately returns to point H. In this connection, the position of element E in the case where no vibration is given is shown in FIG. 22A. The moving direction of heat in the case where element E is moved to the high temperature portion is shown by an arrow (solid line) in FIG. 22B. The moving direction of heat in the case where element E is moved to the low temperature portion is shown by an arrow (solid line) in FIG. 22C.
In this model, heat is moved as follows. When element E, which is present at center C in the case where no vibration is caused, is moved to point H, since the temperature of the circular tube wall at point H is higher than the temperature of element E, element E is given heat from the circular tube wall. When element E is moved by vibration from point H to point L, since the temperature of the circular tube wall at point L is lower than the temperature of element E, element E discharges heat to the circular tube wall.
As described above, heat on the circular tube wall at point H is quickly transported to the circular tube wall at point L via the vibrating fluid (element E). If no vibration is caused, heat is continuously and gradually moved from point H to point L. Therefore, the heat conductivity in this case is much lower than the heat conductivity in the case where the fluid is given vibration. In other words, when the fluid in the circular tube is vibrated, the apparent heat conductivity can be greatly enhanced.
When this heat transport method is used, for example, heat generated from a microprocessor can be quickly diffused. Therefore, it is possible to overcome a problem caused by heat generated in the microprocessor of the note type personal computer.
According to this heat transport method, when the amplitude and period are changed, the apparent heat conductivity can be freely changed. When this function is utilized, for example, when vibration given to the fluid is turned on and off, it becomes possible to make a new device having a heat switch by which heat transport can be turned on and off, which is very convenient.
In this connection, the heat transport system using this heat transport method is in the first stage of development. Therefore, it is necessary for the present inventors to develop a fluid drive unit suitable for used in the heat transport system. In this connection, a pump device such as an actuator, which is operated while being vibrated linearly and used for an artificial heart, is well known as a fluid drive unit.
However, in the heat transport system of the aforementioned principle, fluid is vibrated so as to transport heat, which is a method not used in the conventional heat transport system. Therefore, when only the conventional method of driving fluid is applied to the heat transport system, various problems may be caused.
For example, in the case of vibrating fluid by the conventional method, it is possible to consider a method in which the pump device 80 is connected to one side of the passage as shown in FIG. 23A and the fluid 5 is vibrated from one end of the passage. However, when this method is employed, the following problems may be encountered. Specifically, when this method is employed, a large pressure loss occurs. Therefore, it is difficult to drive the fluid 5 which is charged at an end portion distant from the pump device 80. In particular, when the fluid 5 is sucked to the pump device 80 side, since the fluid 5 charged at the end portion cannot be appropriately sucked to the pump device 80 side, the phenomenon of cavitation occurs in the passage, i.e. bubbles are generated in the passage of the fluid. Further, according to this structure, it is impossible to close the end portion of the passage, and the end portion of the passage cannot be directed downward; in other words, the profile of the passage is restricted.
On the other hand, as shown in FIG. 23B, when the heat transport system is composed in a manner such that two pump devices 80 are respectively arranged at both end portions of the passage and the fluid 5 is driven by the two pump devices 80, it is possible to drive the fluid 5 without causing the phenomenon of cavitation. However, this method has the following disadvantages. According to this system, since the two pump devices 80 are used, the manufacturing cost is raised. Further, since it is necessary to drive the two pump devices 80 synchronously, control of the pump devices 80 becomes complicated.